﻿using System.Net;
using System.Net.Sockets;

namespace ECommon
{
    /// <summary>
    /// 时间工具
    /// </summary>
    public static partial class DatetimeTool
    {
        /// <summary>
        /// 获取iso标准时间
        /// </summary>
        /// <returns>iso标准时间</returns>
        public static DateTime GetIsoNow()
        {
            return DateTime.Parse(DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss"));
        }

        /// <summary>
        /// 获取网络对时
        /// </summary>
        /// <param name="ntpServer">对时服务器</param>
        /// <returns>网络对时</returns>
        public static DateTime GetNetworkTime(string ntpServer = "ntp.ntsc.ac.cn")
        {

            // NTP message size - 16 bytes of the digest (RFC 2030)
            byte[] ntpData = new byte[48];

            //Setting the Leap Indicator, Version Number and Mode values
            ntpData[0] = 0x1B; //LI = 0 (no warning), VN = 3 (IPv4 only), Mode = 3 (Client Mode)

            IPAddress[] addresses = Dns.GetHostEntry(ntpServer).AddressList;

            //The UDP port number assigned to NTP is 123
            IPEndPoint ipEndPoint = new IPEndPoint(addresses[0], 123);
            //NTP uses UDP
            Socket socket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
            socket.Connect(ipEndPoint);

            //Stops code hang if NTP is blocked
            socket.ReceiveTimeout = 3000;
            socket.Send(ntpData);
            socket.Receive(ntpData);
            socket.Close();
            //Offset to get to the "Transmit timestamps" field (time at which the reply
            //departed the server for the client, in 64-bit timestamps format."
            const byte serverReplyTime = 40;
            //Get the seconds part
            ulong intPart = BitConverter.ToUInt32(ntpData, serverReplyTime);
            //Get the seconds fraction
            ulong fractPart = BitConverter.ToUInt32(ntpData, serverReplyTime + 4);
            //Convert From big-endian to little-endian
            intPart = SwapEndianness(intPart);
            fractPart = SwapEndianness(fractPart);
            ulong milliseconds = (intPart * 1000) + ((fractPart * 1000) / 0x100000000L);
            //**UTC** time
            DateTime networkDateTime = (new DateTime(1900, 1, 1, 0, 0, 0, DateTimeKind.Utc)).AddMilliseconds((long)milliseconds);
            return networkDateTime.ToLocalTime();
        }

        /// <summary>
        /// 按位转换无符号长整型为无符号整形
        /// </summary>
        /// <param name="x">无符号长整型</param>
        /// <returns>无符号整形</returns>
        private static uint SwapEndianness(ulong x)
        {
            return (uint)(((x & 0x000000ff) << 24) +
            ((x & 0x0000ff00) << 8) +
            ((x & 0x00ff0000) >> 8) +
            ((x & 0xff000000) >> 24));
        }
    }
}